A SO-DIMM, or Small Outline Dual In-line Memory Module, is a type of computer memory used in notebooks and netbooks today. At first glance, SO-DIMMs may look identical; however there are subtle differences in their design which may keep them from being used interchangeably. These differences will be their pin count and notches.
There are notches at the bottom of SO-DIMMs that specify which type of memory they are. Those notches are also used to make sure the memory is inserted correctly into the computer.
The notch and pin counts of the different types of SO-DIMMs are as follows:
- 100-pin SO-DIMMs have two notches
- 144-pin SO-DIMMs have a single notch near, but not directly at the center
- 200-pin SO-DIMMs have a single notch nearer to one side. The exact location of this notch varies by manufacturer of the memory itself.
- 204-pin SO-DIMMs have a single notch nearer to one side. By the pin count, this indicates that this type of module will be of the DDR3 class of memory.
The 200 pin SO-DIMM will have notches in one of two locations:
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- If the notch is located away from the center, it indicates that this module will be of the DDR class of memory.
- If the notch is located nearer the center of the board, it generally, but not always indicates that this module will be of the DDR2 class of memory.
Note: These two types of 200 pin SO-DIMMs are not interchangeable. The different notch locations are purposely designed to prevent cross-installation.
Note: The dimensions shown are for reference purposes only and are for general comparison. Actual dimensions may vary by manufacturer. This is not an exact technical diagram.
While the type of memory won't matter much for a typical business computer, if your business in engaged in computationally intensive tasks, the performance of your RAM can make a big difference in how fast your computers run. Financial modeling, engineering, and graphics rendering are all business applications that require more RAM than the average, off-the-shelf computer provides. While higher-numbered double-data rate memory is usually faster than lower-numbered versions, there can be some complexities that make this less predictable than you might expect.
SDRAM
To understand the basics of different types of DDR RAM, a basic understanding of how the Synchronous Direct RAM technology on which it is based is helpful. SDRAM is designed to read and write data in conjunction with a clock, which synchronizes the transfer of the data, hence the name. For example, SDRAM operating at a 400MHz clock would be able to interface with the computer and share a chunk of data 400 million times per second.
DDR
The first double data rate RAM modules worked just like SDRAM but with one key difference: Instead of transferring one block of data per clock cycle, they could transfer two. A DDR module running at 400 MHz could theoretically transfer twice as much data as a regular SDRAM module. The downside to this technology was that if a computer missed a clock cycle and didn't transfer memory, it would miss out on twice as much data as with a regular SDRAM module.
DDR Numbers
After the initial generation of DDR, memory manufacturers continued to advance the technology. The numbers associated with DDR, such as DDR2 or DDR4, refer to the generation of the DDR technology used in the memory modules. Newer generations of DDR memory are typically faster than older generations. If you can find two modules with the same speed rating, though, they will usually be able to transfer data at the same rate. For instance, DDR2-800 and DDR3-800 memories both run at 400 MHz and can theoretically transfer 6,400 MB/sec of data. The '800' in their names refers to their 400MHz speed multiplied by two for their double data rate.
Use Ddr4 In Ddr3 Slot
Requirements
There are a couple of requirements that will allow you to use a particular type of memory in your computer. First, your CPU and your motherboard's chipset will need to support both the speed and the manner in which a given type of DDR memory works. Secondly, you must have slots on your mother board that are compatible with your chosen type of memory. Each type of DDR RAM is physically incompatible with the other types. This prevents you from plugging the wrong type of module into your motherboard and damaging it or your computer.
Ddr Ddr2 Ddr3 Difference
The State of the Art
As of the publication date in May of 2013, DDR3 memory is widely available in both desktop and notebook computers. DDR4 memory was displayed in prototype form at the beginning of 2013, and DDR5 is coming, but is not yet available for system memory. DDR5 technology is, however, available in a special type of memory used for graphics cards. Referred to as GDDR5 memory, it has much higher bandwidth than DDR3 and can transfer more data for better graphical rendering.
Ddr2 Vs Ddr3 Memory
Upgrading Your Computer
Choosing memory to upgrade your computer is actually a simpler process than it seems. Since any given computer will only be compatible with a single type of DDR memory, buy the type that works in your computer. If you aren't sure of the exact speed your computer uses, buy the fastest memory available. That way, you can be sure that it'll be fast enough to keep up.
References
About the Author
Ddr2 Vs Ddr3 Ram
Steve Lander has been a writer since 1996, with experience in the fields of financial services, real estate and technology. His work has appeared in trade publications such as the 'Minnesota Real Estate Journal' and 'Minnesota Multi-Housing Association Advocate.' Lander holds a Bachelor of Arts in political science from Columbia University.